摘要
Bitter gourd(fruit of Momordica charantia L.)is a popular vegetable and medical herb known for its intense bitter taste.However,its major bitter-tasting compounds have not been fully characterized.This study aimed to decode its bitterness by application of the sensomics approach.Combining solvent extraction,sensory analysis-guided fractionation and purification with medium-pressure liquid chromatography and high-pressure liquid chromatography,nine bitter-tasting cucurbitane-type triterpenoids were isolated from bitter gourd.The structures of isolated compounds were determined by high-resolution mass spectrometry and nuclear magnetic resonance spectroscopy.The bitter taste recognition thresholds of isolated compounds were in the range from 1.4 mg/L((23E)-3β-O-malonyl-7β,25-dihydroxycucurbita-5,23-dien-19-al,9)to 19.1 mg/L(yeojooside C,5)in 3%ethanol as determined by trained human assessors.Quantification with UPLC-MS/MS demonstrated their natural concentrations in bitter gourd fruits were in the range between 14.2±0.9 mg/kg(yeojooside C,5)and 245.6±22.1 mg/kg(3-O-malonylmomordicine I,10)on a dry weight basis.Calculation of the dose-over-threshold(DoT)factors showed three compounds,namely 3-O-malonylmomordicine I(10),momordicine I(3),and(23E)-3β-Omalonyl-7β,25-dihydroxycucurbita-5,23-dien-19-al(9)were the bitter principles in bitter gourd fruits.On the other hand,momordicoside K(2),which had been known as a bitter principle of bitter gourd for more than forty years,had been proven to be an extraction and isolation artifact rather than a natural component of the plant.Besides,an acid-catalyzed isomerization reaction in the side chain of cucurbitane was discovered,which might explain the formation mechanism of many cucurbitane-type triterpenoids from bitter gourd.
基金
funded by the National Natural Science Foundation of China(No.32302266).
